The present invention relates to a method and an apparatus for the processing of a tubular material web while it is fed through a packing machine, by sealing jaws arranged on both sides of the web and co-operating in pairs. The sealing jaws can be given a reciprocating movement in both the longitudinal direction of the material web and in the transverse direction of the material web.
Packing machines for the manufacture of non-returnable packages for milk or other liquid contents are known. The packing material in general consists of a flexible laminate which comprises layers of paper and thermoplastics and which is supplied to the packing machine in form of a web. The packing laminate is converted in the packing machine to a hose or tube in that the longitudinal edges of the laminate web are sealed to one another in a liquid-tight longitudinal joint. The laminate tube thus formed is filled with the desired contents while it is moved continuously downwards through the packing machine. Thereafter, the tube is sealed in a narrow transverse zone, with the simultaneous forcing out of the contents, by co-operating sealing jaws which are moved towards each other from opposite sides of the tube. As a result the tube is pressed together and the inner thermoplastic layers located opposite each other are made to fuse together through the simultaneous application of heat. The process takes place continuously with the help of two pairs of sealing jaws which alternately process the tube during a simultaneous downward movement and release the tube during an upward return movement. After sealing together and the consequent division of the material tube into individual, closed containers, the containers are separated from one another by cuts in the compressed and sealed zones.
In conjunction with the transverse sealing of the tube, a certain reshaping of the tube is performed in the sense that it is converted from its original, substantially circular cross-sectional shape to a more rectangular cross-sectional shape. This is done with the help of forming jaws connected with the sealing jaws which compress the tube from two sides so that it obtains the desired shape. After separation of the individual, filled and sealed packing containers from each other, a further form-processing usually takes place, so that they acquire a desired final shape, e.g. parallelepipedic.
In this known type of packing machine, the movement of the sealing jaws is guided with the help of several cams which are arranged in succession on a driving shaft located inside the frame of the machine. The driving shaft is connected to an electric driving motor. A number of different cams situated on the driving shaft are connected by a linkage and lever system with the jaws so that these can be given a reciprocating movement in accordance with a given pattern of movement. With the help of different cams, the jaws are moved upwards and downwards in the vertical direction along the longitudinal axis of the tube, and transversely in an opening and closing movement synchronized with the vertical movement. During the downward movement, the jaws are closed and thus press together to advance the material tube, whereas the upwards-directed return movement of the jaws takes place with the jaws in the open, folded out position. The movement of the jaws in the vertical direction is guided by means of fixed guide bars and the different driving movements are transferred with the help of complicated linkages, which make it necessary to provide a relatively large free space along the path of movement of the jaws. Beside this large space, the guiding and driving system also requires accurate adjustment in order to function correctly. However, owing to wear which inevitably arises after a certain period of operation, the inaccuracy of the driving arrangement increases again, and can be counteracted only be renewed adjustment and regular service.
It is an object of the present invention to provide a method of processing a material web which makes it possible to process tubular packing material while avoiding the disadvantages of the known methods.
It is a further object of the present invention to provide a method which makes it possible to continuously process and convert a packing material tube with great and lasting accuracy during a long period of operation.
It is also an object of the present invention to provide a method which simplifies the guiding and driving movements so that wear is minimized and the inaccuracies caused by the same are eliminated.
These and other objects have been achieved in accordance with the invention in that a method for processing a material web including the step of driving the sealing jaws with two driving rods located in parallel with the web. The first driving rod is imparted a reciprocating movement and the second driving rod is imparted a similar reciprocating movement which is superimposed on the movement of the first driving rod.
The method in accordance with the invention permits the guiding and the driving of the sealing jaws to take place by the same elements, namely a number of driving rods parallel with the packing material web which are moved in their longitudinal direction in accordance with a certain pattern of mutual movement. In this way, the space requirement reduced, the design is made simpler and cheaper and the effect of wear on the accuracy is diminished.
By directly connecting the sealing jaws to one another via hook-shaped members during the part of the manufacturing process which normally subjects the driving arrangement to the greatest loads, excessive stresses are avoided which reduces the risk of play and wear, and makes it possible to use smaller machine components.
It is also an object of the present invention to provide an apparatus for the processing of a tubular material web in accordance with the above-mentioned method with the apparatus not being affected by the disadvantages present in similar, previously known apparatus.
It is a further object of the present invention to provide an apparatus for the processing of a tubular material web having a compact design and including as few movable parts as possible.
It is a further object of the present invention to provide an apparatus which subjects the driving and guiding elements to minimum loads and which works with great accuracy even after long periods of operation.
These and other objects have been achieved in accordance with the invention in that an apparatus for the processing of a tubular material web includes sealing jaws arranged on both sides of the web and co-operating in pairs. The sealing jaws can be given a reciprocating movement in the longitudinal direction of the material web and in the transverse direction of the material web. The apparatus also includes a yoke wherein the co-operating jaws are suspended so that they can be swivelled and two parallel driving rods movable in the longitudinal direction of the material web. The first driving rod is connected to the yoke and the second driving rod is connected to the jaws.
Since the movement of the jaws is achieved and is guided by the driving rods parallel with the material web, the transmission of power occurs directly and requires little space. Because the guiding as well as the driving takes place by the said driving rods, only a small number of movable driving and guiding elements are present in the region of the machine which for reasons of hygiene, have to be subjected to frequent rinsing and cleaning.